1. Field of the Invention
This application relates generally to apparatus for monitoring industrial processes, and more particularly relates to a video camera and associated thermal protection apparatus for viewing the interior of a heated chamber.
2. Description of the Related Art
Video cameras are commonly used in CCTV systems associated with the operation and control of industrial processes. The prior art teaches a variety of video camera systems for viewing the interior of a hot, hostile environment, such as a high temperature furnace chamber, through an opening provided in a wall of the chamber. Because a furnace may typically reach temperatures on the order of 2000.degree. F.-3000.degree. F., yet video cameras cannot tolerate temperatures much in excess of 100.degree. F., it is necessary to provide thermal insulation and cooling to prevent damage to the video camera.
In the customary approach, the prior art utilizes an elongated steel tube, extending through the opening in the wall of the high temperature chamber. The tube contains a series of spaced optical elements, including lenses, to form a relay tube. The camera is positioned outside or near the outside of the chamber wall, and the series of optical elements transmit the image and focus it on the camera away from the hot, hostile environment. Relay lens tubes or relay tubes of this type typically may range from 2 feet long to 20 feet long.
One difficulty with such prior art systems is that the high temperatures and the variations in temperature make it extremely difficult to maintain the close tolerances which are necessary for accurately transmitting the image through the relay tube. These thermal stresses cause relative movement of the relay tube components, thereby introducing image distortion. Additionally, each lens or optical element introduces some distortions as a result of its imperfections. Consequently, video systems utilizing such lens tubes have limited performance and are expensive, demanding high quality lenses in order to obtain and maintain the formation of an image of acceptable quality.
Another difficulty with such prior art systems arises from the fact that there are a variety of different furnaces, and consequently such systems require the availability of numerous lens tubes to accommodate the variabilities of different installations. The need to design and to construct a variety of lens tubes further increases cost.
It is therefore an object and feature of the present invention to eliminate the typical lens tube and its relay optics and position the camera at the interior end of a thermally protective tube structure in order to eliminate the costs and problems associated with a relay lens tube and improve the image quality, while providing a cooling and thermal isolation system capable of maintaining the camera environment at a temperature on the order of 100.degree. F. or less. Elimination of the relay lens tube not only enhances the quality of the available image, but also eliminates the requirement for and therefore the cost of the design and maintenance of a broad variety of relay lens tubes for different installations.